Multivariate analysis of the relationship of six variables to blood pressure: Findings from Chicago Community Surveys, 1965–1971

Abstract

1. 1. Four multivariate statistical methods—partial correlation, multiple cross classification, multiple logistic regression, and multiple linear regression—were used to study the relationship between six variables and blood pressure in over 13,000 men and women, white and black, ages 30–44 and 45–64 surveyed in two low-income Chicago communities. The analyses were carried out separately for eight age-sex-race groups. The six variables were relative weight, resting heart rate, plasma glucose 1 hr after 100 g oral load, hematocrit, serum cholesterol and age. 2. 2. The first three of these variables—relative weight, heart rate, and plasma glucose —were independently related to blood pressure with a high degree of consistency, with p values for statistical significance ≤0.001. 3. 3. Hematocrit was independently and additively related to diastolic—but not to systolic—pressure for the four age-race groups of women, but only for one of the four age-race groups of men. 4. 4. The findings with respect to serum cholesterol and blood pressure were generally negative. 5. 5. Even within the narrow age groups studied—ages 30–44 and 45–64—age was significantly related to systolic level particularly ( p values ≤0.01 or ≤0.001), independent of the five other variables. 6. 6. When multivariate regression equations and their coefficients, computed from the experience of an entire age-sex-race group, were used to calculate an expectation of elevated blood pressure for each person, and then persons were ordered from low to high in expectation, a high proportion of all persons with recorded elevations of blood pressure were in the highest decile and quintile of expected prevalence—e.g. for persons age 30–44 in the four sex-race groups, from 47–69 per cent of observed cases with diastolic pressure ≥95 mm Hg were in the highest quintile (20 per cent) of expected prevalence. The observed prevalence of elevated blood pressure was as much as 20 times as high for the highest quintile of expected prevalence as for the lowest. A similar but less effective concentration of cases of elevated blood pressure was obtained with the multiple cross classification method, by dichotomizing four of the independent variables and identifying the substratum with any two, three or all four high.